The present embodiments relate to single photon emission computed tomography (SPECT). SPECT imaging uses a radioisotope or radiotracer to determine physiological function within a patient. For example, the uptake of the radiotracer by tissues in the body is measured. The emissions from the radiotracer are detected. The activity concentration (i.e., the concentration of the radiotracer from different locations) is reconstructed from the detected emissions.
For quantitative SPECT imaging, reliable (both accurate and precise) estimates of activity concentration and uptake values are desired. Given various modeling and unknowns in SPECT, general use of quantitative SPECT has been limited. For example, quantitative SPECT is only realized in industry for Tc-99m, which has a single emission energy. Quantitative imaging of radionuclides with multiple emissions (e.g., I-123, Lu-177 and In-111) or simultaneous imaging of multiple tracers (e.g. cardiac imaging for Tc-99m MIBI and I-123 MIBG) may have important applications in nuclear medicine, but the emissions at different energies may degrade the imaging.